Conventionally, a car navigation system has been known which can issue various instructions using voice recognition. Although a car navigation system without using the voice recognition makes genre specification by selecting from a menu displayed, the car navigation system using the voice recognition can specify the genre by speaking a genre name or the like, for example, even if the menu is invisible such as during driving.
Since the voice recognition is a technique capable of recognizing only the vocabulary recorded in a voice recognition dictionary in advance, it is necessary for a user to pronounce the word representing the genre correctly when inputting for the voice recognition. However, since the number of genres to be searched in the car navigation system generally amounts to several tens, it is difficult for the user to memorize the genres available in the car navigation system. In addition, it is difficult to distinguish the genres available in the car navigation system from genres the user sees in everyday life such as in yellow pages or the Internet or from genres available in other car navigation systems.
As a relevant technique, Patent Document 1 discloses a voice recognition system capable of good voice recognition even if an input object such as a facility name is pronounced rather inaccurately. In the voice recognition system, a map data storage means stores formal names of facilities as basic words. In a voice recognition unit, derivative key character strings in a basic word are detected, and the basic word is changed in part using the key character strings. Thus, a derivative word representing the same facility as the basic word in another expression is generated automatically. For example, a basic word “Shizuoka Prefectural Susono High School” includes key character strings “Shizuoka Prefectural” and “High School”. Then, derivative words such as “Susono High School” and “Susono Senior High” are generated. The voice recognition is carried out by applying such a derivative word or basic word to an object of recognition. Accordingly, it is sufficient to store one word for each object.    Patent Document 1: Japanese Patent Laid-Open No. 11-202891/1999.
As for the conventional voice recognition system applied to the car navigation system, although it has the foregoing problem, it stores in its voice recognition dictionary only the vocabulary expressing retrievable genres as a function of the car navigation system. Accordingly, if the user utters a word representing a genre unavailable in the car navigation system, it will mistake the word for another word, which causes a problem in that the car navigation system operates in a manner different from that the user intends.
The present invention is implemented to solve the foregoing problem. Therefore it is an object of the present invention to provide a voice recognition system capable of preventing a system working in response to the recognition from operating in a manner different from that the user intends.